The present invention relates to a heat-curable coating composition based on prepolymers having ketoxime-blocked NCO groups and cross linkers from the group of particular amines. In particular, the present invention relates to the use of such coating compositions, defined in detail in the following, for producing protective coatings on substrates, especially metal parts. This protective layer may be present alone or as a component of a paint system of several layers.
Coating compositions consisting of prepolymers with at least 2 blocked isocyanate groups and an average molecular weight of between 500 and 25,000, aliphatic and/or cycloaliphatic and/or aromatic amines with at least 2 primary and/or secondary amino groups, stable aqueous polymer dispersions and/or polymer solutions, as well as optionally organic solvents, are known (German Offenlegungsschrift No. 2,184,079). Such coating composition are used preferably for coating nonwoven textile fabrics. This is also the case for heat-curable coating compositions, which are known from the German Offenlegungsschrift No. 2,902,090 and which contain prepolymers having ketoxime-blocked NCO groups and an average molecular weight of 1,000 to 15,000, a cross linker of the formula ##STR1## in which R represents hydrogen or a methyl group, as well as optionally gigments, fillers, blowing agents and other known additives.
These known coating compositions have the disadvantage that either they are not very reactive, that is, they require a high baking temperature, or, when they are highly reactive, they have an unsatisfactory shelf life.